block: add bdrv_graph_wrlock_drained() convenience wrapper

Many write-locked sections are also drained sections. A new
bdrv_graph_wrunlock_drained() wrapper around bdrv_graph_wrunlock() is
introduced, which will begin a drained section first. A global
variable is used so bdrv_graph_wrunlock() knows if it also needs
to end such a drained section. Both the aio_poll call in
bdrv_graph_wrlock() and the aio_bh_poll() in bdrv_graph_wrunlock()
can re-enter a write-locked section. While for the latter, ending the
drain could be moved to before the call, the former requires that the
variable is a counter and not just a boolean.

Since the wrapper calls bdrv_drain_all_begin(), which must be called
with the graph unlocked, mark the wrapper as GRAPH_UNLOCKED too.

The switch to the new helpers was generated with the following
commands and then manually checked:
find . -name '*.c' -exec sed -i -z 's/bdrv_drain_all_begin();\n\s*bdrv_graph_wrlock();/bdrv_graph_wrlock_drained();/g' {} ';'
find . -name '*.c' -exec sed -i -z 's/bdrv_graph_wrunlock();\n\s*bdrv_drain_all_end();/bdrv_graph_wrunlock();/g' {} ';'

Suggested-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
Message-ID: <20250530151125.955508-25-f.ebner@proxmox.com>
[kwolf: Removed redundant GRAPH_UNLOCKED]
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 5 insertions, 15 deletions

diff --git a/block.c b/block.c
index bfd4340b24..1da10d55f0 100644
--- a/block.c
+++ b/block.c
@@ -1721,14 +1721,12 @@ bdrv_open_driver(BlockDriverState *bs, BlockDriver *drv, const char *node_name,
 open_failed:
     bs->drv = NULL;
 
-    bdrv_drain_all_begin();
-    bdrv_graph_wrlock();
+    bdrv_graph_wrlock_drained();
     if (bs->file != NULL) {
         bdrv_unref_child(bs, bs->file);
         assert(!bs->file);
     }
     bdrv_graph_wrunlock();
-    bdrv_drain_all_end();
 
     g_free(bs->opaque);
     bs->opaque = NULL;
@@ -3602,11 +3600,9 @@ int bdrv_set_backing_hd(BlockDriverState *bs, BlockDriverState *backing_hd,
     int ret;
     GLOBAL_STATE_CODE();
 
-    bdrv_drain_all_begin();
-    bdrv_graph_wrlock();
+    bdrv_graph_wrlock_drained();
     ret = bdrv_set_backing_hd_drained(bs, backing_hd, errp);
     bdrv_graph_wrunlock();
-    bdrv_drain_all_end();
 
     return ret;
 }
@@ -3797,12 +3793,10 @@ static BdrvChild *bdrv_open_child_common(const char *filename,
         return NULL;
     }
 
-    bdrv_drain_all_begin();
-    bdrv_graph_wrlock();
+    bdrv_graph_wrlock_drained();
     child = bdrv_attach_child(parent, bs, bdref_key, child_class, child_role,
                               errp);
     bdrv_graph_wrunlock();
-    bdrv_drain_all_end();
 
     return child;
 }
@@ -5180,8 +5174,7 @@ static void bdrv_close(BlockDriverState *bs)
         bs->drv = NULL;
     }
 
-    bdrv_drain_all_begin();
-    bdrv_graph_wrlock();
+    bdrv_graph_wrlock_drained();
     QLIST_FOREACH_SAFE(child, &bs->children, next, next) {
         bdrv_unref_child(bs, child);
     }
@@ -5189,7 +5182,6 @@ static void bdrv_close(BlockDriverState *bs)
     assert(!bs->backing);
     assert(!bs->file);
     bdrv_graph_wrunlock();
-    bdrv_drain_all_end();
 
     g_free(bs->opaque);
     bs->opaque = NULL;
@@ -5515,8 +5507,7 @@ int bdrv_append(BlockDriverState *bs_new, BlockDriverState *bs_top,
     assert(!bs_new->backing);
     bdrv_graph_rdunlock_main_loop();
 
-    bdrv_drain_all_begin();
-    bdrv_graph_wrlock();
+    bdrv_graph_wrlock_drained();
 
     child = bdrv_attach_child_noperm(bs_new, bs_top, "backing",
                                      &child_of_bds, bdrv_backing_role(bs_new),
@@ -5537,7 +5528,6 @@ out:
 
     bdrv_refresh_limits(bs_top, NULL, NULL);
     bdrv_graph_wrunlock();
-    bdrv_drain_all_end();
 
     return ret;
 }